1. Field of the Invention
This invention relates to a lighttight envelope used when a stimulable phosphor sheet used in a radiation image recording and reproducing system for recording a radiation image in the stimulable phosphor sheet and then reproducing a visible image therefrom is conveyed in a high-speed image recording apparatus. This invention particularly relates to a lighttight envelope for high-speed conveyance of the stimulable phosphor sheet, which has a configuration for improving the operating efficiency in handling of the stimulable phosphor sheet.
2. Description of the Prior Art
High-speed image recording apparatuses have heretofore been used for angiography and the like. The high-speed image recording apparatuses record X-ray images of objects on many X-ray films by sequentially projecting the X-ray images onto the X-ray films. The apparatuses are suitable particularly for sequentially recording angiograms, which change from time to time, on many X-ray films when the diffusion speed of the contrast media is different among the objects.
In the high-speed image recording apparatuses, the X-ray film is used in the form sandwiched, for example, between two intensifying screens and housed in a flexible lighttight envelope.
The high-speed image recording apparatus using a lighttight envelope in which an X-ray film is housed comprises a first film receiving section for receiving the unexposed lighttight envelopes, a conveyance mechanism for sequentially conveying the lighttight envelopes at high speeds from the first film receiving section to an image recording position where the X-ray films are exposed to X-rays passing through an object, and for sequentially conveying the exposed lighttight envelopes at high speeds from the image recording position, and a second film receiving section for receiving the exposed lighttight envelopes which are conveyed at high speeds from the image recording position. The object is positioned on the high-speed image recording apparatus.
The lighttight envelope used in the high-speed image recording apparatus constituted as described above has a configuration for sufficiently shielding the X-ray film from light. FIG. 1A is a perspective view showing an example of the lighttight envelope employed in the conventional high-speed image recording apparatus using an X-ray film, and FIG. 1B is a perspective view showing the lighttight envelope of FIG. 1A with the inlet opened. Sufficiently lighttight, black plastic sheets 2A and 2B are heat-sealed at their sides 20, 21 and 22 to form an envelope open at one side. The open side of the plastic sheet 2A continues into an opening edge portion 2a, and the open side of the plastic sheet 2B continues into an opening edge portion 2b. A face-to-face fastener 2c consisting of a tape provided with many fine hook-like fibers and a tape provided with many fine loop-like fibers is positioned so that the tapes extend on the inner surfaces of the opening edge portions 2a and 2b over the entire lengths thereof. The opening edge portions 2a and 2b are lighttightly engaged with each other by the face-to-face fastener 2c. As indicated by a chain line in FIG. 1A, an X-ray film 25 sandwiched between a pair of intensifying screens (not shown) is housed inside of the sealed sides 20, 21 and 22 and the face-to-face fastener 2c. Thus the X-ray film 25 is handled and conveyed in a condition sufficiently shielded from light.
The conventional lighttight envelope as described above houses the X-ray film 25 in the sufficiently lighttight condition and is loaded into the high-speed image recording apparatus. However, since the face-to-face fastener 2c positioned at the opening edge portions 2a and 2b for securing sufficient lighttightness strongly closes the opening through which the X-ray film 25 is inserted into and removed from the lighttight envelope and since the area of the opening is small, insertion and removal of the X-ray film 25 are not easy to conduct.
Recently, a radiation image recording and reproducing system using a stimulable phosphor as described below has been proposed.
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultra-violet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibitinhg such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined patent publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as photographic film or on a display device such as a cathode ray tube (CRT).
This radiation image recording and reproducing system using the stimulable phosphor sheet is advantageous over conventional radiography using an X-ray film and intersifying screens in that the radiation image can be recorded over a very wide range (latitude) of radiation exposure and further in that the electric signal used for reproducing the visible image can be freely processed to improve the image quality for viewing, particularly for diagnostic purposes. In more detail, since the amount of light emitted upon stimulation after the radiation energy is stored in the phosphor varies over a very wide range in proportion to the amount of energy stored therein, it is possible to obtain an image having desired density regardless of the amount of exposure of the phosphor to the radiation by reading out the emitted light with an appropriate read-out gain and converting it to an electric signal to reproduce a visible image on a recording medium or a display device. The electric signal may further be processed as desired to obtain a radiation image suitable for viewing, particularly for diagnostic purposes. This is very advantageous in practical use.
Also in the aforesaid radiation image recording and reproducing system using the stimulable phosphor sheet, if such a high-speed image recording apparatus as used in the conventional radiography could be employed, it would become possible to quickly record many radiation images having an improved image quality, particularly a high diagnostic efficiency and accuracy. This would be very advantageous for medical diagnosis.
As mentioned above, the high-speed image recording apparatus is suitable particularly for angiography. Therefore, if the high-speed image recording apparatus could be employed for the radiation image recording and reproducing system using the stimulable phosphor sheet, it would become possible to further improve the diagnostic efficiency and accuracy of angiograms. This would be very advantageous for medical diagnosis.
Accordingly, it is desired to use the aforesaid lighttight envelope for the X-ray film in the high-speed image recording apparatus employed for the radiation image recording and reproducing system, and to load the stimulable phosphor sheet into the high-speed image recording apparatus in the form housed in the lighttight envelope.
However, the aforesaid lighttight envelope is not convenient for inserting the stimulable phosphor sheet thereinto and removing it therefrom at a high operating efficiency. Further, in the radiation image recording and reproducing system using the stimulable phosphor sheet, the stimulable phosphor sheet need not be shielded from light before an X-ray image is recorded thereon. Also, the required degree of light shielding for the stimulable phosphor sheet after an X-ray image is recorded thereon is far lower than the degree of light shielding required for the X-ray film. Therefore, it is not advantageous from the viewpoint of operating efficiency to employ the conventional lighttight envelope for the X-ray film directly as a lighttight envelope for the stimulable phosphor sheet.
In view of the aforesaid feature of the radiation image recording and reproducing system using the stimulable phosphor sheet, a need exists for a lighttight envelope for high-speed conveyance of the stimulable phosphor sheet, which exhibits a comparatively simple light shielding function and which has a configuration facilitating insertion and removal of the stimulable phosphor sheet.